In recent years, magnetic recording/reproducing apparatuses are being designed to have a higher recording density in order to achieve a large capacity with a small size. In the field of a hard disk device, which is a typical magnetic recording/reproducing apparatus, the recording density is rapidly increasing at the rate of 100% per year. As the technical background for enabling such a high recording density, significant factors include the improvement in the linear recording density achieved by the improvement in the performance of a magnetic recording medium and a head-disk interface, as well as the appearance of a new signal processing mode such as a partial response.
In recent years, however, the tendency toward an increase in the track density significantly exceeds that of the linear recording density, thus improving the areal recording density. This is due to the fact that a magneto-resistive type head, which has a much improved reproduction output performance compared with a conventional inductive type magnetic head, has come into practical use. At present, with the practical use of the magneto-resistive type head, a signal with a track width in the sub micron range can be reproduced with a high S/N ratio.
In order for a magnetic head to trace such narrow tracks accurately and to reproduce signals at a high S/N ratio, the tracking servo technology of the magnetic head plays an important role. Such a tracking servo technology is described in detail in, for example, “Yamaguchi: Highly Accurate Servo Technology of Magnetic Disk Apparatus, Journal of the Magnetics Society, Vol. 20, No. 3, pp. 771 (1996)”.
FIG. 32 is a plan view showing a configuration of a conventional magnetic disk device 90. The magnetic disk device 90 has a disk-shaped magnetic disk 8. The magnetic disk 8 is rotated by a motor (not shown).
The magnetic disk device 90 has a head arm 225 pivotably provided around a pivot axis 226. At the tip of the head arm 225, a head suspension 222 is provided. On the tip of the head suspension 222, a magnetic head 221 is mounted. The magnetic disk device 90 is provided with a voice coil motor 223 for driving the head arm 225 in a way in which the voice coil motor 223 is placed on the opposite side of the head arm 225 with respect to the pivot axis 226 disposed therebetween.
In the magnetic disk device 90 having such a configuration, when the head arm 225 is driven by the voice coil motor 223, the head arm 225 pivots around the pivot axis 226. Therefore, the magnetic head 221 mounted on the head suspension 222 moves on the rotating magnetic disk 8 along an arc-shaped tracking scanning orbit 224 having the pivot axis 226 as its center.
According to the document mentioned above, a magnetic disk provided for the magnetic disk device has regions (hereafter referred to as “preformat recording region”) spaced at predetermined angles over a revolution of a disk, that is, over an angle of 360 degrees. In the preformat recording region, as shown in FIG. 33, a synchronous signal pattern 211, a sector mark pattern 212, an address information signal pattern 213 and a tracking servo signal pattern 214, etc. are recorded. Thus, the magnetic head, based on these patterns, reproduces signals at every predetermined period to verify its position and corrects its displacement in the radial direction of the magnetic disk as required, thus tracing a track correctly.
Prerecording the above-mentioned preformat information signal patterns (master information) such as the synchronous signal pattern 211, the sector mark pattern 212, the address information signal pattern 213 and the tracking servo signal pattern 214, etc. is referred to as a preformat recording. A master information magnetic recording technology that is a technology enabling the preformat recording in a short time is disclosed in JP 10 (1998)-40544A. This master information magnetic recording technology enables the preformat recording in a short time.
Herein, a method for prerecording master information on a magnetic disk will be explained. First, a magnetic disk is magnetized in one direction, thus initializing the magnetic disk. Next, the master information carrier on which ferromagnetic thin film patterns are formed is brought into contact with the magnetic disk. The ferromagnetic pattern herein denotes a pattern corresponding to an information signal to be preformat-recorded. For example, in the case of preformat-recording signals shown in FIG. 33, the ferromagnetic pattern is a pattern corresponding to FIG. 33. Thereafter, a magnetic field (referred to as a transfer field) is applied from the outside to the magnetic disk with which the master information carrier is brought into contact.
Note here, it is desirable that the direction of the magnetic field at the time of initialization is a direction opposite to the direction of the transfer field. The ferromagnetic thin film patterns formed on the master information carrier are magnetized. The magnetic field is weakened at the part facing the ferromagnetic thin film patterns on the master information carrier and strengthened at a part that does not face the ferromagnetic thin films on the master information carrier. Therefore, on the magnetic disk, the part that does not face the ferromagnetic thin film on the master information carrier is magnetized in the direction of the transfer field; and the part corresponding to the part facing the ferromagnetic thin film on the master information carrier is not magnetized by the transfer field and the direction of magnetization at the time of initialization is maintained. Consequently, at the edge of the ferromagnetic thin film on the master carrier, magnetization reversal occurs. Thus, it is possible to record a magnetization pattern corresponding to the ferromagnetic thin film patterns formed on the master carrier in the magnetic recording medium.
Thus, the master information magnetic recording causes the magnetization reversal along the edge of the ferromagnetic thin film pattern on the master information carrier. Therefore, in order to obtain excellent reproduced signals, it is desirable that the direction of the transfer field approximates the direction perpendicular to the edge of the ferromagnetic thin film on the master carrier.
Herein, a line parallel to the direction of the relative movement between the magnetic head and the magnetic disk due to a rotation of the magnetic disk is referred to as a pattern angle reference; and an angle made by the pattern angle reference and the ferromagnetic thin film pattern formed on the master information carrier is referred to as a pattern angle. In general, this pattern angle differs according to the radial position of the disk.
The pattern angle is an angle made by a tangent of an arc showing an orbit on which the magnetic head on the pivoting head arm moves and the moving direction of the head, which is perpendicular to the radial direction of the magnetic disk. Therefore, the pattern angle gradually changes from the inner circumference to the outer circumference of the magnetic disk.
On the other hand, JP 11 (1999)-273069A proposes that the direction of the transfer field is to be a direction of the normal to the arc that is a moving orbit of the magnetic head (hereafter, referred to as “head orbit”), thereby improving the signal recorded in the magnetic disk.
The general preformat pattern includes a plurality of different patterns that are constituting elements thereof, such as a synchronous signal pattern, a sector mark pattern, an address information signal pattern, and a tracking servo signal pattern, etc., which are sequentially disposed in the moving direction of a magnetic head. Each kind of the patterns is formed along the head orbit. Therefore, if the radial position is the same, the pattern angles of each pattern are the same.
However, in some preformat patterns, plural types of patterns sequentially existing toward the moving direction of the head have different pattern angles, respectively. A typical example of such a pattern is a tracking servo signal corresponding to the phase detection method. The phase detection method is proposed in, for example, JP60 (1985)-10472A, JP8 (1996)-221919A, etc. This phase detection method is a detection method which is not likely to be affected by noise and can obtain the position error signal with high accuracy. Therefore, in the case where the track density is much more increased in the future, the method is becoming an important method capable of corresponding to the improvement of the positioning accuracy of the head.
FIG. 34 is an enlarged view for explaining a configuration of another preformat information signal patterns, which is to be formed on a conventional master information carrier as ferromagnetic thin film patterns. This ferromagnetic thin film pattern 94 corresponds to a preformat pattern of the phase detection method disclosed in the JP8 (1996)-221919A mentioned above.
The ferromagnetic pattern 94 includes a synchronous signal pattern 95, a sector mark pattern 91, an address information signal pattern 98, a tracking servo signal pattern 96 and a tracking servo signal pattern 97. The servo signal pattern 97 is formed tilting with respect to the servo signal pattern 96. Therefore, when the magnetic head shifts along the radial direction of the magnetic disk, the position of a pulse gradually changes. Therefore, a phase difference occurs between the servo signal pattern 96 and the servo signal pattern 97.
All of the synchronous signal pattern 95, the sector mark pattern 91, the address information signal pattern 98 and the servo signal pattern 96, which are included in this ferromagnetic thin film pattern 94, are formed along the head orbit. Therefore, when the radial position is the same, these patterns have the same pattern angles.
However, the servo signal pattern 97 is formed tilting with respect to these patterns and therefore it has a pattern angle that is different from that of these patterns.
In this case, as mentioned above, when the direction of the transferr field is to be a direction of the normal to the head orbit, the normal line with respect to the edge of the ferromagnetic thin film on the master information carrier corresponding to the servo signal pattern 97 and the direction of the transfer field are displaced from each other. Therefore, the magnetic field change lacks sharpness at the edge of the ferromagnetic thin film on the master information carrier. As a result, the position of the magnetization reversal, that is, the position of a pulse becomes unclear. This causes the phase disturbance of signals, thus making the highly accurate positioning of the head by the phase detection method difficult. Furthermore, the effective strength of the transfer field with respect to the servo signal pattern 97 is different from that with respect to the other patterns. As a result, it becomes difficult to set an appropriate transfer field condition for all patterns having different pattern angles. When recording with an appropriate transfer field cannot be carried out, the reproduction output decreases.
The problems such as the phase disturbance of signals or the reduction of the reproduction output as mentioned above become more serious as the displacement of the transfer field direction with respect to the direction perpendicular to the ferromagnetic substance on the master information carrier becomes larger.
That is, in the preformat pattern in which plural types of patterns having different pattern angles are present in the moving direction of a magnetic head, it becomes important to achieve the quality of signals acceptable for practical use by minimizing the phase disturbance of signals or reduction of the reproduction output.
It is an object of the present invention to provide a master information recording apparatus capable of enhancing the reliability of recording preformat patterns and a magnetic recording medium on which information is recorded using the same from the view point of the above-mentioned problems.